Crosslinked proppant-gel matrix

ABSTRACT

A method of making a proppant-gel matrix comprising: a) hydrating a gelling agent to form a hydrated gelling agent; b) adding a basic compound to the hydrated gelling agent to form a basic hydrated gelling agent having a pH in the range of 11.5 to 14.0; c) mixing the basic hydrated gelling agent and a proppant to form a basic hydrated gelling system; and d) adding a crosslinking agent to the basic hydrated gelling system to form the proppant-gel matrix, is disclosed. The proppant-gel matrix can then be used as a fracturing fluid in a hydraulic fracturing process.

RELATED APPLICATION DATA

This application is a continuation application of co-pending U.S.application Ser. No. 15/612,560, with a filing date of Jun. 2, 2017, ofwhich the entire contents of the applications are incorporated byreference herein.

FIELD OF THE INVENTION

This invention relates to hydraulic fracturing processes. Moreparticularly, this invention relates to fracturing fluids useful inhydraulic fracturing processes.

BACKGROUND OF THE INVENTION

In a hydraulic fracturing (‘fracking’) operation in an oilfield, highpressure fluid is pumped to the downhole formation to create fractures.After the pressure is released, the newly created fractures will beclosed due to formation pressure. To prevent the closure, proppants arepumped into the downhole formation which hold the newly createdfractures. Generally, a gelling agent such as guar gum is used as acarrier to transport the proppants. In this operation, proppants such assands, coated sands, and ceramics are blended with the guar gum, and thesuspension is pumped into the downhole formation. The carrier is thendegraded and the proppants remain.

Proppant loading is an important factor in determining the cost of ahydraulic fracturing operation. For a given well, the required proppantamount is a fixed number, which is determined by the volume of fracturesgenerated by the fracturing operation. The more proppants that can beloaded per pound of gelling agent, the less gelling agent will beneeded, and the cheaper the operation will be. In addition to the costof the gelling agent, less energy will be used if less pump time isneeded, which saves money on equipment consumption, thereby alsoreducing the operation cost. However, the proppant loading per pound ofgelling agent is limited by the inherent density of the proppants. Theproppants are physically suspended in the gelling agent, and thesettling occurs instantly after the agitation is stopped. Increasingproppant loading will result in more settling. Proppants settled in awellbore can clog the wellbore, which is highly undesirable. Quicksettling also makes it difficult to transport proppants to the locationsthat are near the far end of the cracks, which has been believed to becritical to the production rate. Increasing gel viscosity can increaseproppant loading, but increased gel viscosity is associated withincreased gelling agent loading. Also, increasing gel viscosity willincrease pump loading, thereby shortening pump life, and thus is not aneffective method.

Therefore, a more efficient system that can transport more proppantswith lower raw material, energy, and operational costs would bedesirable.

SUMMARY OF THE INVENTION

In one broad embodiment of the present invention, there is disclosed amethod of making a proppant-gel matrix comprising, consisting of, orconsisting essentially of: a) hydrating a gelling agent to form ahydrated gelling agent; b) adding a basic compound to the hydratedgelling agent to form a basic hydrated gelling agent having a pH in therange of 11.5 to 14.0; c) mixing the basic hydrated gelling agent and aproppant to form a basic hydrated gelling system; and d) adding acrosslinking agent to the basic hydrated gelling system to form theproppant-gel matrix.

Also disclosed in the present invention is a method for stimulatinghydrocarbon production from a subterranean formation comprisinginjecting a fracturing fluid comprising the above-mentioned proppant-gelmatrix into the subterranean formation.

BRIEF DESCRIPTION OF THE FIGURES

FIG. 1 is a diagram showing variables useful in an equation to calculatethe settling rate of samples.

FIG. 2 is a plot of settling rate vs. initial pH of samples over a 24hour period.

FIG. 3 is a plot of settling rate vs. initial pH of samples over a 48hour period.

FIG. 4 is a plot of settling rate vs. initial pH of samples over a 72hour period.

FIG. 5 is a plot of settling rate vs. initial pH of samples over a 96hour period.

FIG. 6 is a plot of viscosity vs. initial pH of samples.

DETAILED DESCRIPTION OF THE INVENTION

In one broad embodiment of the invention, there is disclosed a method ofmaking a proppant-gel matrix comprising: a) hydrating a gelling agent toform a hydrated gelling agent; b) adding a basic compound to thehydrated gelling agent to form a basic hydrated gelling agent having apH in the range of 11.5 to 14.0, c) mixing the basic hydrated gellingagent and a proppant to form a basic hydrated gelling system; and d)adding a crosslinking agent to the basic hydrated gelling system to formthe proppant-gel matrix.

Generally, the gelling agent may be present in the proppant-gel matrixan amount in the range of from 0.01 weight percent to about 5 weightpercent, and the crosslinking agent can be present in the proppant-gelmatrix in an amount in the range of from 0.003 weight percent to 5weight percent, based on the total weight of aqueous fluid in theproppant-gel matrix, with the proviso that the weight percents of allcomponents in the aqueous fluid add up to 100 weight percent. Theproppant can generally be present in the proppant-gel matrix in therange of from 2 weight percent to 60 weight percent based on the totalweight of the proppant-gel matrix, with the proviso that the weightpercents of all components in the proppant-gel matrix add up to 100weight percent.

Examples of gelling agents that can be used include, but are not limitedto guar gum, modified guar gum such as hydroxypropyl guar, hydroxyethylguar, carboxymethyl guar, carboxymethyl hydroxypropyl guar,carboxymethylhydroxyethyl guar, and cellulose and its derivatives suchas hydroxyethyl cellulose, carboxyethylcellulose,carboxymethylcellulose, carboxymethylhydroxyethylcellulose, and othernatural gums such as natural gums obtained from seaweeds such as, forexample, agar, alginic acid, sodium alginate, and carrageenan. Naturalgums obtained from non-marine botanical resources can also be used.Examples of these include, but are not limited to gum arabic, from thesap of Acacia trees, gum ghatti, from the sap of Anogeissus trees, gumtragacanth, from the sap of Astragalus shrubs, karaya gum, from the sapof Sterculia trees, locust bean gum, from the seeds of the carob tree,beta-glucan, from oat or barley bran, chicle gum, obtained from chicletrees, dammar gum, from the sap of Dipterocarpaceae trees, glucomannan,from the konjac plant, mastic gum, obtained from the mastic tree,psyllium seed husks, from the Plantago plant, spruce gum, obtained fromspruce trees, and tara gum, from the seeds of the tara tree. Naturalgums produced by bacterial fermentation such as gellan gum, and xanthangum can also be used. Gelling agents can also include any other naturalor synthetic oligomeric or polymeric thickeners that contain a cis-diolstructure in the molecule. Combinations of any of the above-mentionedgelling agents can also be used.

The gelling agent can be present in the proppant-gel matrix of thepresent invention in an amount sufficient to provide the desiredviscosity and strength to hold and deliver the proppants to the desireddestinations. Generally, the gelling agent may be present in an amountin the range of from 0.01 weight percent to about 5 weight percent,based on the total weight of the aqueous fluid of the proppant-gelmatrix. In various other embodiments, the gelling agent is present in anamount in the range of from 0.01 weight percent to 2 weight percent,based on the total weight of the aqueous fluid in the proppant-gelmatrix.

Generally, the desired degree of hydration for the gelling agent is from5 percent to 100 percent. Any and all ranges between 5 and 100 percentare included herein and disclosed herein, for example, the gelling agentcan be hydrated to a degree of from 10 percent to 85 percent, 20 percentto 60 percent, 30 percent to 60 percent, or 40 percent to 60 percent.

After the desired degree of hydration is achieved, a basic compound canbe added to the hydrated gelling agent to form a basic hydrated gellingagent having a pH in the range of from 11.5 to 14.0. Any and all pHranges between 11.5 and 14.0 are included herein and disclosed herein;for example, the basic hydrated gelling agent can have a pH in the rangeof from 12.0 to 14.0, from 12.2 to 13.5, from 12.0 to 13.0, from 12.3 to13.0, from 12.0 to 12.8, from 12.3 to 12.8, from 12.2 to 12.9, from 12.2to 12.8, from 12.3 to 12.9, from 12.3 to 13.0, from 12.4 to 12.8, orfrom 12.4 to 12.6.

A basic compound is any compound which produces hydroxide ions in watersolutions. Examples of basic compounds that can be useful at this stageinclude, but are not limited to bases such as sodium hydroxide,potassium hydroxide, lithium hydroxide, cesium hydroxide, rubidiumhydroxide, ammonium hydroxide, magnesium hydroxide, calcium hydroxide,barium hydroxide, sodium carbonate, sodium bicarbonate, potassiumcarbonate, potassium bicarbonate, rubidium carbonate, rubidiumbicarbonate, cesium carbonate, cesium bicarbonate, potassium phosphate,sodium phosphate, cesium phosphate, lithium phosphate, and combinationsof any two or more thereof.

The basic hydrated gelling agent can then be mixed with a proppant toform a basic hydrated gelling system.

Proppants useful in this invention include, but are not limited to rawsand (such as brown sand or white sand), sand coated with variouscoatings such as phenolic coatings, polyurethane coatings, polyamidecoatings, polyester coatings, epoxy coatings, any other useful polymercoatings, small molecule coating additives with molecular mass below1,000 grams/mole such as SandWedge® and Expedite®, both available fromHalliburton, ceramic proppants, ceramic proppants coated with resincoatings, polymer coatings, or small molecule coating additives, andproppants made of any other useful inorganic raw materials. Mixtures ofany of the aforementioned proppants can also be used.

The proppants can have a grain size from 3 mesh to 500 mesh. Any and allranges within the range of 3 mesh to 500 mesh are included herein anddisclosed herein; for example, the proppants can have a grain size offrom 3 mesh to 400 mesh, from 10 mesh to 400 mesh, from 15 mesh to 300mesh or from 20 mesh to 200 mesh.

Generally, the proppant is present in the proppant-gel matrix in therange of from 2 weight percent to 60 weight percent, based on the totalweight of the proppant-gel matrix. Any and all ranges within the rangeof 2 weight percent to 60 weight percent are included herein anddisclosed herein; for example, the proppant can be present in theproppant-gel matrix in the range of from 5 weight percent to 50 weightpercent, or from 15 weight percent to 45 weight percent.

In various embodiments, above-mentioned steps b) and c) can be performedin reverse, ie. the proppant can be added to the hydrated gelling agentbefore the basic compound is added to the system.

A crosslinking agent is then added to the basic hydrated gelling systemto form a proppant-gel matrix.

Examples of crosslinking agents include, but are not limited to boratessuch as borax (sodium borate) and boric acid, other boron compounds suchas probertite (NaCaB₅O₉.5H₂O), ulexite (BaCaB₅O₉.8H₂O), nobleite(CaB₆O₁₀.4H₂O), gowerite (CaB₆O₁₀.5H₂O), frolovite (Ca₂B₄O₈.7H₂O),colemanite (Ca₂B₆O₁₁.5H₂O), meyerhofferite (Ca₂B₆O₁₁.7H₂O), inyoite(Ca₂B₆O₁₁.13H₂O), priceite (Ca₄B₁₀O₁₉.7H₂O), tertschite (Ca₄B₁₀O₁₉.20),ginorite (Ca₂B₁₄O₂₃.8H₂O), pinnoite (MgB₂O₄.3H₂O), paternoite(MgB₈O₁₃.4H₂O), kurnakovite (Mg₂B₆O₁₁.15H₂O), inderite (Mg₂B₆O₁₁.15H₂O),preobrazhenskite (Mg₃B₁₀O₁₈.41/2H₂O), hydroboracite (CaMgB₆O₁₁.6H₂O),inderborite (CaMgB₆O₁₁.11H₂O), kaliborite (Heintzite) (KMg₂B₁₁O₁₉.9H₂O),veatchite (SrB₆O₁₁.2H₂O), trialkoxy boron ester, and any other boroncompound that can generate borate, or boric acid at a pH range of from11.5 to 14.0.

Other examples of crosslinking agents include, but are not limited to,titanium alkanol amine complexes, titanium diethanolamine complexes,titanium triethanolamine complexes, titanium lactate, titanium ethyleneglycolate, titanium acetyleacetonate, titanium ammonium lactate,titanium diethanolamine lactate, titanium triethanolamine lactate,titanium diisopropylamine lactate, titanium sodium lactate salts,titanium sorbitol complexes, zirconium triisopropylamine, zirconiumlactate, zirconium lactate triethanolamine, zirconium carbonate,zirconium oxide, zirconium acetylacetonate, zirconium malate, zirconiumcitrate, or a polyhydroxy complex zirconium. Other titanates andzirconates such as those in the Tyzor™ line from Dorf Ketal can also beused. Other examples of crosslinking agents that can be used arechromium, aluminum, and antimony compounds, and any other compounds thatcan form bis-diol complexes.

Combinations of any of the above-mentioned crosslinking agents can alsobe used.

The crosslinking agent can be present in the proppant-gel matrix anamount in the range of from 0.003 weight percent to 5 weight percent,based on the total weight of aqueous fluid in the proppant-gel matrix.Any and all ranges between 0.003 weight percent to 5 weight percent areincluded herein and disclosed herein; for example, the crosslinkingagent can be present in the range of from 0.003 weight percent to 2weight percent or 0.05 weight percent to 1.5 weight percent.

Optionally, the proppant-gel matrix can further contain other additivesthat are known to be commonly used in hydraulic fracturing operations bythose skilled in the art. Examples of these additives include, but arenot limited to surfactants, gel breakers, oxygen scavengers, alcohols,scale inhibitors, corrosion inhibitors, fluid-loss additives, H₂Sscavengers, and bactericides.

Examples of gel breakers that can be used include, but are not limitedto potassium persulfate, sodium peroxydisulfate, ammoniumperoxydisulfate, t-butylhydroperoxide, calcium peroxide, magnesiumperoxide, sodium chlorite, sodium bromate, andethylenediaminetetraacetic acid, and combinations of any two or morethereof.

The method of this invention can be employed in standard fracturingtreatments, employing techniques and equipment well known in the art.

EXAMPLES

For the following examples, the data was derived in accordance with thefollowing procedures.

The settling rate was calculated using the following equation:% settle=H/(Ht−Hs)×100

The variables H, Ht, and Hs are measured according to the diagram inFIG. 1.

The viscosity of the bulk fluid was measured with a Brookfieldviscometer.

Example 1—Effect of pH on the Stability of the Matrix

General Procedure

To a glass jar with 250 mL of distilled water was added 0.6 grams ofguar. The system was agitated manually to disperse the guar. Afterhydrating for 30 minutes at ambient temperature, the pH of the fluid wasadjusted by adding sodium hydroxide solution (50%). 45 grams of proppant(40/70 Unimin white sand) was added to the fluid and the system wasbriefly mixed. 0.9 grams of borax solution (20% in glycol) was thenadded to the fluid, and the system was manually agitated for 5 minutes.The settling time was recorded, the level of the proppant was measuredand the settling rate was calculated. The settling rate is the quotientof the settled height of the proppant divided by the original height.

The settling rate was measured for 4 samples. The pH values weremeasured at the beginning of the settling experiment. The pH values ofthe 4 samples were: 11.4, 12.0, 12.1, and 12.5. The settling percentagesof these samples is shown in Table 1, below.

TABLE 1 Effect of pH on Settling Rate of Sand in the Guar Gel Matrix %settling at % settling at % settling at % settling at sample pH 24 h 48h 72 h 96 h 1 11.4 100 2 12.0 24 60 100 3 12.1 15 32 45 70 4 12.5 7 1928 42

FIGS. 2, 3, 4, and 5 also show the settling rate for the samples after24 hours, 48 hours, 72 hours, and 96 hours, respectively. As can be seenfrom these figures, the pH has a dramatic impact on the settling rate ofthe proppants.

FIG. 6 is a plot of viscosity vs. pH for the four samples. As can beseen from FIG. 6, the effect of pH on the viscosity of the samples isminor.

Example 2—pH Ranges

General Procedure

To a glass jar with 125 mL deionized water was added 0.3 grams of guargum. The guar was quickly stirred so as to be distributed in the waterwithout visible particles. The system was allowed to remain at ambienttemperature for 30 minutes in order to hydrate. The fluid was thenadjusted to a designated pH by adding NaOH solutions (10% for initialadjustment, 0.5% for fine adjustment). 90 grams of sand (40/70 Uniminwhite sand) and 0.9 grams of borax (20% in ethylene glycol) were thenadded to the fluid.

This experiment was conducted with samples with pH values of 9.0, 9.5,10.0, 10.5, 11.0, 11.5, 12.0, 12.5 and 13.0. Table 2 below shows thesettling percentages of these samples.

TABLE 2 Effect of pH on Settling Rate of Sand in Guar Gel Matrix % % % %% % % % settling settling settling settling settling settling settlingsettling Sample pH at 1 h at 3 h at 18 h at 3 d at 4 d at 7 d at 18 d at27 d 1 9.0 34 56 100 2 9.5 34 56 100 3 10.0 34 56 100 4 10.5 34 56 100 511.0 34 56 100 6 11.5 N/A N/A N/A 100 7 12.0 N/A N/A N/A 80 100 8 12.5N/A N/A N/A 20 21 27 34 52 9 13.0 N/A N/A N/A 16 25 28 63 72

Table 2 shows that with a pH up to 11.0, there is no cross-linkingbetween the sand and the guar since all the samples show the samesettling rate.

Example 3—Narrower pH Ranges

General Procedure

To a glass jar with 125 ml deionized water was added 0.3 grams of guargum. The guar was quickly stirred to be distributed in the water withoutvisible particles. The system was allowed to remain at ambienttemperature for 30 minutes in order to hydrate. The fluid was thenadjusted to a designated pH by adding NaOH solutions (10% for initialadjustment, 0.5% for fine adjustment). 90 grams of 40/70 Unimin whitesand and 0.9 grams of borax solution (20% in ethylene glycol) was addedto the fluid, and the fluid was manually mixed for 5 minutes.

This experiment was conducted with samples with pH values of 12.000,12.117, 12.228, 12.313, 12.408, 12.502, 12.602, 12.699, 12.825, and12.897. Table 3 shows the settling percentage of the samples at 4 days,10 days, 20 days, and 30 days, respectively. The data in Table 3demonstrates that samples having a pH value of 12.408 and 12.502, thematrix was the most stable. After 30 days, these samples settled 25.0%and 22.6% respectively.

TABLE 3 Settling Percentages vs. Time % % % % settling settling settlingsettling sample pH at 4 d at 10 d at 20 d at 30 d 1 12.000 100.0 — — — 212.117 27.7 100.0 — —  3* 12.228 20.9 n/a n/a n/a 4 12.313 8.2 20.7 46.976.7 5 12.408 7.3 11.7 19.0 25.0 6 12.502 7.0 11.0 16.0 22.6 7 12.6027.0 12.1 20.0 41.3  8** 12.699 3.4 7.3 16.0 30.3 9 12.825 6.0 12.1 31.750.1 10  12.897 7.0 16.4 49.4 51.7 3*: on the 6^(th) day, the sampleshowed abnormal settling, possibly caused by bacteria contamination.8**: post-agitation was applied, which indicates agitation profile canchange settling rate.

Example 4—Matrix Thermal Stability

In order to test the thermal stability of the guar-boron-silica matrix,three samples with different pH values were prepared according to theprocedure in Example 2. After the samples were aged for 10 minutes, theywere then placed in a water bath at 60° C. The samples were removed fromthe bath every 10 minutes for photography. As shown in Table 4, sample 3showed about 10 times more stability compared to sample 1.

Table 4. Settling Time vs. pH at 60° C.

TABLE 4 Settling Time vs. pH at 60° C. 100% settle time, Sample pH min 110.212 10 2 12.000 38 3 12.400 96

Example 5—Effectiveness of Gel Breaker

To test the effectiveness of a routine gel breaker, a pair of sampleswere prepared, one containing the gel breaker potassium persulfate (2lbs per thousand gallon), and the other without the gel breaker. Thesamples were prepared in the following manner: to a glass jar with 120ml deionized water was added 0.3 grams of guar gum. The guar was quicklystirred to be distributed in the water without visible particles. Thesystem was allowed to remain at ambient temperature for 30 minutes inorder to hydrate. The fluid was then adjusted to a pH value of 12.5 byadding NaOH solutions (10% for initial adjustment, 0.5% for fineadjustment). 45 grams of 40/70 Unimin white sand and 0.9 grams of boraxsolution (20% in ethylene glycol) was added to the fluid, and the fluidwas manually mixed for 5 minutes.

The samples were placed in an oven with a temperature between 60-80° C.It was found that the sample with the gel breaker was completely brokenat 18 minutes, and the sand fell to the bottom of the jar. Meanwhile,the sample without the gel breaker only settled about 20%. This testsuggests that an oxidizer gel breaker is still effective for theguar-boron-proppant matrix.

While the present invention has been described and illustrated byreference to particular embodiments and examples, those of ordinaryskill in the art will appreciate that the invention lends itself tovariations not necessarily illustrated herein.

The invention claimed is:
 1. A method of making a proppant-gel matrixcomprising: a) hydrating a gelling agent to form a hydrated gellingagent; b) adding a basic compound to the hydrated gelling agent to forma basic hydrated gelling agent having a pH in the range of 11.5 to 14.0;c) mixing the basic hydrated gelling agent and a proppant to form abasic hydrated gelling system; and d) adding a crosslinking agent to thebasic hydrated gelling system to crosslink the proppant with the gellingagent to form a proppant-gel matrix.
 2. A method in accordance withclaim 1 wherein the gelling agent is selected from the group consistingof guar gum, hydroxypropyl guar, hydroxyethyl guar, carboxymethyl guar,carboxymethyl hydroxypropyl guar, carboxymethylhydroxyethyl guar,hydroxyethyl cellulose, carboxyethylcellulose, carboxymethylcellulose,carboxymethylhydroxyethylcellulose, agar, alginic acid, sodium alginate,carrageenan, gum arabic, gum ghatti, gum tragacanth, karaya gum, locustbean gum, beta-glucan, chicle gum, dammar gum, glucomannan, mastic gum,psyllium seed husks, spruce gum, tara gum, gellan gum, xanthan gum, andcombinations thereof.
 3. A method in accordance with claim 1 wherein theproppant is selected from the group consisting of raw sand,phenolic-coated sand, polyurethane-coated sand, polyamide-coated sand,polyester-coated sand, small molecule additive-coated sand, ceramics,resin-coated ceramics, polymer-coated ceramics, small moleculeadditive-coated ceramics, and combinations thereof.
 4. A method inaccordance with claim 1 wherein the crosslinking agent is selected fromthe group consisting of borax, boric acid, probertite, ulexite,nobleite, gowerite, frolovite, colemanite, meyerhofferite, inyoite,priceite, tertschite, ginorite, pinnoite, paternoite, kurnakovite,inderite, preobrazhenskite, hydroboracite, inderborite, kaliborite,veatchite, trialkoxy boron ester, a titanium alkanol amine complex, atitanium diethanolamine complex, a titanium triethanolamine complex,titanium lactate, titanium ethylene glycolate, titaniumacetyleacetonate, titanium ammonium lactate, titanium diethanolaminelactate, titanium triethanolamine lactate, titanium diisopropylaminelactate, titanium sodium lactate salts, a titanium sorbitol complex,zirconium triisopropylamine, zirconium lactate, zirconium lactatetriethanolamine, zirconium carbonate, zirconium oxide, zirconiumacetylacetonate, zirconium malate, zirconium citrate, a polyhydroxyzirconium complex, and combinations thereof.
 5. A method in accordancewith claim 1 wherein the proppant is added to the hydrated gelling agentprior to step b) or wherein the proppant is added in step c).
 6. Amethod in accordance with claim 1 wherein the gelling agent is presentin an amount in the range of from 0.01 weight percent to 5 weightpercent, based on the total weight of aqueous fluid in the proppant-gelmatrix.
 7. A method in accordance with claim 1 wherein the proppant ispresent in an amount in the range of from 2 weight percent to 60 weightpercent, based on the total weight of the proppant-gel matrix.
 8. Amethod in accordance with claim 1 wherein the crosslinking agent ispresent in an amount in the range of from 0.003 weight percent to 5weight percent, based on the total weight of aqueous fluid in theproppant-gel matrix.
 9. A method in accordance with claim 1 wherein thebasic compound is selected from the group consisting of sodiumhydroxide, potassium hydroxide, lithium hydroxide, cesium hydroxide,rubidium hydroxide, ammonium hydroxide, magnesium hydroxide, calciumhydroxide, barium hydroxide, sodium carbonate, sodium bicarbonate,potassium carbonate, potassium bicarbonate, rubidium carbonate, rubidiumbicarbonate, cesium carbonate, cesium bicarbonate, potassium phosphate,sodium phosphate, cesium phosphate, lithium phosphate, and combinationsof any two or more thereof.
 10. A method in accordance with claim 1wherein the proppant is sand and the sand comprises sand grains with ameasurement in the range of from 3 to 500 mesh.
 11. A method inaccordance with claim 1 wherein the proppant-gel matrix is added to afracturing fluid.
 12. A method in accordance with claim 1 wherein thecrosslinking agent is selected from the group consisting of chromiumcompounds, aluminum compounds, and antimony compounds.
 13. A method inaccordance with claim 1 wherein the proppant comprises grains with ameasurement in the range of from 10 mesh to 400 mesh.
 14. A method inaccordance with claim 1 wherein the proppant is present in an amount inthe range of from 5 weight percent to 50 weight percent, based on thetotal weight of the proppant-gel matrix.
 15. A method in accordance withclaim 1 wherein the crosslinking agent is present in an amount in therange of from 0.003 weight percent to 2 weight percent, based on thetotal weight of aqueous fluid in the proppant-gel matrix.
 16. A methodin accordance with claim 1 wherein: the proppant is present in an amountin the range of from 15 weight percent to 45 weight percent, based onthe total weight of the proppant-gel matrix; and the crosslinking agentis present in an amount in the range of from 0.05 weight percent to 1.5weight percent, based on the total weight of aqueous fluid in theproppant-gel matrix.
 17. A method of making a proppant-gel matrixcomprising: a) hydrating a gelling agent to form a hydrated gellingagent; b) adding a basic compound to the hydrated gelling agent to forma basic hydrated gelling agent having a pH in the range of 11.5 to 14.0,the basic compound comprising a compound which produces hydroxide ionsin water solutions; c) mixing the basic hydrated gelling agent and asand proppant to form a basic hydrated gelling system; and d) adding acrosslinking agent to the basic hydrated gelling system to crosslink thesand proppant with the gelling agent to form a sand proppant-gel matrix,wherein the gelling agent is selected from the group consisting of guargum, modified guar gum, and combinations thereof, the crosslinking agentcomprising a boron compound.
 18. The method in accordance with claim 17,wherein: the sand proppant comprises sand grains with a measurement inthe range of from 20 to 200 mesh; and the boron compound is selectedfrom the group consisting of borax, boric acid, or s combinationthereof.